A semiconductor dynamic quantity sensor is generally made by processing a semiconductor substrate to form a moving electrode and a fixed electrode apart from and facing each other, and detects an applied dynamic quantity such as an acceleration or an angular velocity on the basis of capacitance changes between the moving electrode and the fixed electrode accompanying displacement of the moving electrode when the dynamic quantity is applied.
For example, a semiconductor acceleration sensor has been proposed in JP-A-9-113534 (hereafter “Patent Document 1”) in which a supporting substrate made of a semiconductor serves as a fixed electrode and a moving electrode made of a semiconductor and displaceable in the thickness direction of the supporting substrate is disposed above one side of the supporting substrate, apart from and facing it, and which detect an applied acceleration on the basis of capacitance changes occurring between the moving electrode and one side of the supporting substrate when the acceleration is applied. In Patent Document 1, the moving electrode is rectangular and its four corners are anchored by flexible spring parts forming the shape of a swastika.
A semiconductor acceleration sensor of this kind has also been proposed in JP-A-10-178184 (hereafter “Patent Document 2”) in which a combtooth shaped moving electrode and a combtooth shaped fixed electrode face each other in a meshing state and which detect the application of acceleration in the horizontal direction of the semiconductor substrate.
However, in capacitance-type semiconductor dynamic quantity sensors of this kind, improvements in detection sensitivity are needed, and to achieve these improvements, it is necessary to increase the capacitance between the moving electrode and the fixed electrode, that is, the detection capacitance.
This detection capacitance can be increased by increasing the electrode sizes and thereby increasing the facing area of the electrodes; however, increasing the facing area like this causes the problem of increased size of the sensor.